** FILE **This undated family file photo provided by the Law Offices of John Burris shows Oscar Grant, a 22-year-old transit rider who was shot and killed by BART police on New Year's Day, 2009. A Douglas County jail official confirmed that 27-year-old Johannes Mehserle, who was involved in the incident, was in custody Tuesday night, Jan. 14, 2009, under a fugitive warrant issued in California (AP Photo/Family Handout provided by the Law Offices of John Burris) ** NO SALES **

Photo: AP

** FILE **This undated family file photo provided by the Law...

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A copy of a portrait of Oscar Grant taken last month was on display as attorney John Burris, representing the family of Oscar Grant, slain by a BART police officer New Year's Day, held a press conference near his office in Oakland, Calif. on January 4, 2009.

Photo: Courtesy Of Johnson Family

A copy of a portrait of Oscar Grant taken last month was on display...

The imprisoned father of Oscar Grant, the unarmed rider shot to death by a BART police officer early New Year's Day, has filed a federal civil rights lawsuit against the transit agency.

Oscar Grant Jr., who is serving a prison sentence for murder, seeks unspecified damages in the suit, filed Friday in U.S. District Court in San Francisco by Oakland attorney Panos Lagos.

Grant's son, Oscar Grant III, 22, of Hayward and several other young men were pulled off a Dublin-Pleasanton train by police investigating reports of a fight. The younger Grant was facedown on the station platform when he was shot by Officer Johannes Mehserle.

Mehserle, 27, quit the BART force Jan. 7 and was ordered in June to stand trial for murder. His attorney said Mehserle had meant to fire his Taser when he fired a single shot with his pistol.

Grant Jr. cried in his prison cell at California State Prison, Solano in Vacaville when he learned that his son had been killed, Lagos said today.

Grant Jr. was convicted of murder a month after his son was born. A jury found him guilty of the Sept. 8, 1985, slaying of Anthony Epps, 24, who was shot to death while watching TV in his home on Darien Avenue in East Oakland. A woman who was with Epps was critically wounded.

"Even though he is a convicted murderer, I would hope that people could still identify and appreciate that there's still a relationship between father and son," Lagos said.

The lawsuit is the second filed against BART in the case. In March, attorney John Burris filed a federal civil rights suit on behalf of Grant III's mother, Wanda Johnson, as well as Sophina Mesa, who was Grant's girlfriend and is raising the couple's 4-year-old daughter.

An attorney for BART in civil court has said Grant's death was "a tragic accident," citing Mehserle's explanation about trying to fire his Taser.